1. Filed of the Invention
This invention relates to a high frequency push-pull transformer, and more particularly to a push-pull transformer which is suitable to be used in a high frequency push-pull transformer amplifier.
2. Description of the Prior Art
The major portions of a high frequency push-pull amplifier comprises, as shown in FIG. 3, a high frequency push-pull transformer 10 which is disposed on the input side, an amplifying transistor circuit 20, and a high frequency push-pull transformer 30 which is disposed on the output side.
The high frequency push-pull transformers 10 and 30 which are respectively disposed on the input side and output side have circuits of the same structure. The push-pull transformer 30 on the output side is connected in such a manner as to be disposed inversely with respect to the push-pull transformer 10 on the input side, which means that the input terminal thereof will be disposed inversely with respect to that of the push-pull transformer 10.
A conventional push-pull transformer 10 is shown in FIG. 4, in which reference numeral 11 represents a coaxial input line, reference numeral 11A represents an internal conductor of the coaxial line 11, and reference numeral 11B represents an outer conductor of the coaxial line 11. Stubs 12 and 13 are connected to the internal conductor 11A and the outer conductor 11B, respectively. The length of each of the stubs 12 and 13 is determined in such a manner that they each become quarter-wavelength line with respect to the frequency range for use.
The output from the internal conductor 11A and that from the outer conductor 11B are respectively supplied to output lines 16 and 17 through direct current cutting capacitors 14 and 15, respectively. In this figure, the output lines 16 and 17 are expressed in the form of a microstrip line.
The push-pull transformer 10 shown in FIG. 4 is needed to constitute a high frequency push-pull amplifier, and output terminals 18A and 18B thereof respectively issue outputs of the same amplitude which have a phase difference of 180.degree. from each other. The output from each of the output terminals 18A and 18B is introduced to and amplified by the corresponding transistors or vacuum tubes.
The electric power amplified by the vaccuum tubes or transistors is, as shown in FIG. 3, bound into one by means of the similar push-pull transformer 30. The above components constitute a push-pull amplifier. Reference numeral 10A represents an input terminal.
However, in the above described push-pull transformer 10, the length of each of the stubs 12 and 13 is limited to one quarter of the wavelength of the frequency used. The overall reflection coefficient increases with other frequencies. Therefore, determination of the frequency used determines the size of the stubs 12 and 13. For example, if this circuit is intended to be used in a relatively low frequency range, the size of the stubs 12 and 13 increases, causing the overall size of the high frequency push-pull amplifier which includes these stubs to become large too, which means that handling of the same becomes difficult as well.